Folding step stool



FIG. 1 is a perspective view of a folding step stool design;

FIG. 2 is a top view thereof;

FIG. 3 is a left side view, which is a mirror image of the right side view thereof;

FIG. 4 is a bottom view thereof;

FIG. 5 is a front view thereof; and,

FIG. 6 is a rear view thereof.

The broken lines shown represent unclaimed subject matter and form no part of the claimed design. 

CLAIM The ornamental design for a folding step stool, as shown and described. 